I recently purchased a 64oz bottle of Arista Liquid Film Developer (Clayton Chemical) for my photo I class. I mixed the half gallon concentrate 1:9 for stock solution. My students developed several rolls of the same 35mm Arista 400iso film using the "stock" 1:9 solution. Some rolls turned out just fine but some rolls look underdeveloped. My students swear their temperatures (20˚C) and times have been consistent. Although, I assumed that the word "concentrate" meant I could mix the entire bottle (5 gal) to a "stock" solution, so my students would not have to worry about measurements at this point. I am wondering if this so called "stock" solution is really a diluted "working" solution, and has simply exhausted in a period of 7 days. Please tell me this is simply not true. I plan on doing some clip tests tomorrow. I store the developer in a refrigerator @ 11-15˚C. Thanks.

It's best to only mix enough working strength film developer just before it is required and to store the rest of the developer as the original concentrate.
Use the working strength developer once only and then discard it.

Clayton Chemical makes ARISTA PREMIUM FILM DEVELOPER (BLACK BOTTLE).
If this is the product that you purchased, contact me and I will make you satisfied with our product.
Lowell Huff
310 538 9530askus@claytonchem.com